Since objects to be incinerated such as wood chips, bark, textile wastes, rice hulls, and scrap paper have large water-absorbing properties, their variations in the moisture content are largely depending on seasons, the weather conditions, and the like, so that it has been difficult to completely burn out objects to be incinerated which have different water contents in an incinerator of a definite construction.
As for incinerators, for instance, multi-stage furnaces have generally been used for sewage sludge having a low heating value; stoker furnaces for objects to be incinerated with a heating value of 1,000 kcal/kg or above; and stationary hearth furnaces of small-scale designed for objects to be incinerated with a heating value of 4,000 kcal/kg or above.
However, conventional incinerators have drawbacks, respectively, and, for instance, multi-stage furnaces have particularly weak points with respect to variations in the properties of objects to be incinerated; stoker furnaces with respect to synthetic resin products; and stationary hearth furnaces with respect to objects to be incinerated having a large ash content. These incinerators also have common weak points with respect to variations in the water content and to objects to be incinerated in which nonflammable or flame-resisting objects are mixed.
In addition, it has been difficult for conventional incinerators to completely burn out objects to be incinerated having large water contents unless auxiliary fuel is used. Furthermore, since a combustion exhaust gas is released as it is to the air via a flue, conventional incinerators are not provided with means for making effective use of the exhaust gas secondarily.